It's no surprise that more folks are streaming movies and "binge-watching" shows on Internet-based sites like Netflix, Hulu and Amazon. But a new study from Nielsen out Wednesday tries to measure just how prevalent so-called "over-the-top" services that don't rely on cable or satellite TV have become.

Though precise viewership data is kept secret by those companies, a July survey of 2,000 consumers, half of whom use Netflix, allowed Nielsen to venture some estimates:

• 38% of Americans "use or subscribe" to Netflix, up from 31% last year, although Netflix claims only about 30 million subscribing households.

• 18% use Hulu, up from 12% last year, with 12% saying they use the free version and 6% using the subscription-based Hulu Plus.

• And 13% said they use Amazon Prime Instant Video, nearly double the 7% who said so last year.

The study also found 88% of Netflix users reported watching three or more episodes of a TV show in a single day, and 45% said they watch original series on streaming services, such as Netflix's Emmy-nominated House of Cards.

Among Netflix users, 48% watch on a computer screen (up from 44% last year); 23% watch on a smartphone (up from 11%); 15% watch on their iPad, way up from 5% last year. But the percentage of users who reported using Roku or Nintendo's Wii game console dropped this year, reflecting the declining popularity of those devices.